#define _GNU_SOURCE
#include <stdlib.h>
#include <string.h>
#include <search.h>

/*
open addressing hash table with 2^n table size
quadratic probing is used in case of hash collision
tab indices and hash are size_t
after resize fails with ENOMEM the state of tab is still usable

with the posix api items cannot be iterated and length cannot be queried
*/

#define MINSIZE 8
#define MAXSIZE ((size_t)-1/2 + 1)

struct __tab {
    ENTRY *entries;
    size_t mask;
    size_t used;
};

static struct hsearch_data htab;

static int __hcreate_r(size_t, struct hsearch_data *);
static void __hdestroy_r(struct hsearch_data *);
static int __hsearch_r(ENTRY, ACTION, ENTRY **, struct hsearch_data *);

static size_t keyhash(char *k)
{
    unsigned char *p = (void *)k;
    size_t h = 0;

    while (*p)
        h = 31*h + *p++;
    return h;
}

static int resize(size_t nel, struct hsearch_data *htab)
{
    size_t newsize;
    size_t i, j;
    ENTRY *e, *newe;
    ENTRY *oldtab = htab->__tab->entries;
    ENTRY *oldend = htab->__tab->entries + htab->__tab->mask + 1;

    if (nel > MAXSIZE)
        nel = MAXSIZE;
    for (newsize = MINSIZE; newsize < nel; newsize *= 2);
    htab->__tab->entries = calloc(newsize, sizeof *htab->__tab->entries);
    if (!htab->__tab->entries) {
        htab->__tab->entries = oldtab;
        return 0;
    }
    htab->__tab->mask = newsize - 1;
    if (!oldtab)
        return 1;
    for (e = oldtab; e < oldend; e++)
        if (e->key) {
            for (i=keyhash(e->key),j=1; ; i+=j++) {
                newe = htab->__tab->entries + (i & htab->__tab->mask);
                if (!newe->key)
                    break;
            }
            *newe = *e;
        }
    free(oldtab);
    return 1;
}

int hcreate(size_t nel)
{
    return __hcreate_r(nel, &htab);
}

void hdestroy(void)
{
    __hdestroy_r(&htab);
}

static ENTRY *lookup(char *key, size_t hash, struct hsearch_data *htab)
{
    size_t i, j;
    ENTRY *e;

    for (i=hash,j=1; ; i+=j++) {
        e = htab->__tab->entries + (i & htab->__tab->mask);
        if (!e->key || strcmp(e->key, key) == 0)
            break;
    }
    return e;
}

ENTRY *hsearch(ENTRY item, ACTION action)
{
    ENTRY *e;

    __hsearch_r(item, action, &e, &htab);
    return e;
}

static int __hcreate_r(size_t nel, struct hsearch_data *htab)
{
    int r;

    htab->__tab = calloc(1, sizeof *htab->__tab);
    if (!htab->__tab)
        return 0;
    r = resize(nel, htab);
    if (r == 0) {
        free(htab->__tab);
        htab->__tab = 0;
    }
    return r;
}
weak_alias(__hcreate_r, hcreate_r);

static void __hdestroy_r(struct hsearch_data *htab)
{
    if (htab->__tab) free(htab->__tab->entries);
    free(htab->__tab);
    htab->__tab = 0;
}
weak_alias(__hdestroy_r, hdestroy_r);

static int __hsearch_r(ENTRY item, ACTION action, ENTRY **retval, struct hsearch_data *htab)
{
    size_t hash = keyhash(item.key);
    ENTRY *e = lookup(item.key, hash, htab);

    if (e->key) {
        *retval = e;
        return 1;
    }
    if (action == FIND) {
        *retval = 0;
        return 0;
    }
    *e = item;
    if (++htab->__tab->used > htab->__tab->mask - htab->__tab->mask/4) {
        if (!resize(2*htab->__tab->used, htab)) {
            htab->__tab->used--;
            e->key = 0;
            *retval = 0;
            return 0;
        }
        e = lookup(item.key, hash, htab);
    }
    *retval = e;
    return 1;
}
weak_alias(__hsearch_r, hsearch_r);
